A series of individual parts – is this a paradox?

A US-American medical device manufacturer has focused on the care of patients suffering from irreversible ankle trauma. These bone defects are usually caused by disease or accidents, as seen in the case of a 60-year-old patient who shattered her talus bone in a bad accident. It turned out that there was no satisfactory treatment option for this fracture, at least not if the bone needed to be replaced. Three months after her injury, the patient's only option was to have the ankle stiffened. Unfortunately, this is still the case for many people in this situation.

For this reason, our customer has developed a customized fitting option that promises an alternative way out. A patient-specific implant provides a fast, affordable, and perfectly fitting replacement for the talus bone in severe cases, thus restoring the functionality of the ankle joint. To do this, this innovative application exploits the full potential of additive manufacturing. Each implant has an individual geometry and is, therefore, to be treated as a one-off, but is manufactured as a series product responding to individual customer requirements. At the same time, special lightweight components are integrated that cannot be manufactured using conventional processes. This places high demands on process stability, process monitoring, and product quality in manufacturing. With our ADM-CV solution, FIT has the right process for these requirements.

The road from CT scan to implant

The production of each patient-specific implant starts with the anatomical data of the respective patient. They are collected directly by our customer as the distributor. For this purpose, the ankle joint is scanned in a computer tomograph (CT) and the resulting data model is processed so that it is a perfect copy of the defective bone. In the 3D model, implant specialists then add so-called volume placeholders to certain bone contact surfaces. The so-prepared file is sent directly to FIT.

The data experts at FIT first replace the placeholders with predefined lattice structures that imitate the structure of the bone as closely as possible. Lightweight areas and solid areas alternate in such a way that the various requirements for the implant (stable osseointegration or low-friction joint mobility) are met. Subsequently, the 3D model is checked by FEM simulations to ensure the load-bearing capacity of the implant.

After the final design approval by the customer, additive manufacturing starts using electron beam melting (EBM or PBF-EB/M). Compared to laser melting (LM or PBF-LB/M), EBM has the advantage of a production under a vacuum. This avoids the inclusion of oxygen in the component during production, resulting in a density of up to 99.8%. The implants are made of titanium Grade 5. Titanium is an inert material, which means that it does not react with the body. Therefore, it is a perfectly suitable material for bone implants. Compared to material alternatives such as cobalt chrome, titanium has also significantly less weight, which is an additional advantage for the implant.

3D printing is immediately followed by production-related post-processing, i.e. the implant is blasted and freed from its support structures. These connection points are then ground and the sliding surfaces of the implant are milled. The so-prepared areas are polished to a high gloss using a special process known as "mirror finish". The implant is then cleaned by ultrasound and passed on to quality assurance.

The special process requirements

The special challenge in this project is to manufacture implants as series products under cost and quality aspects, but at the same time to treat them as unique patient-specific specimens. At FIT, this is achieved by the ADM-CV solution. This makes it possible for us to:

• deliver a patient-specific implant to the USA within 7 working days from the time the data is received.
• integrate complex lattice structures on the bone contact surfaces that make the implant lighter while providing better osseointegration.
• produce perfect surfaces on the sliding surfaces of the implant using mirror finish so that optimal movement function is achieved.
• produce an additional trial implant or a patient-specific drill and cutting guide in PA 12 from selective laser sintering (SLS or PBF-LB/P) according to ISO 9001 to improve the preparation for surgery.
• guarantee manufacturing costs that enable the US-American medical device manufacturer to profitably use the implants to treat patients.

To tell you the good ending of the story, after going through surgery and recovery, the patient quickly was able to begin to walk freely again, returning to a normal way of life. "Being able to walk again is just priceless", she says happily.

FIT offers a fully integrated value chain for the production of your patient-specific titanium implants. From data service to additive manufacturing to professional post-processing, we are your one-stop shop for patient care fulfilling all individual requirements. So, do not take any risks, rely on an experienced specialist when it comes to the additive manufacturing of titanium implants.